Some buildings have roofs that are shingled. Some others have membrane roofs, in which a flexible membrane forms the outer environmental barrier. Many membrane roofs are flat or slightly sloped or arched. In general, roofing membranes are secured over rigid insulation boards, such as foam boards, that increase the thermal barrier properties of the roof.
Membrane roofs, like other roofs, must withstand severe environmental conditions, including high winds and hail. Winds can cause large pressure differentials across the roof membrane, and can actually lift or separate the membrane from the roof.
Wind uplift occurs when the air pressure below the roof system is greater than that above the system as wind flows over the building decreasing the pressure directly above the roof surface. The atmospheric pressure below the roof attempts to equalize this pressure differential, causing an upward push of air referred to as wind uplift.
The Underwriters Laboratories has developed a standard uplift test, the UL580 uplift test, to test the ability of membrane roofing constructions to withstand the high uplift forces that can be caused by high winds.
FM Global Approval LLC also provides uplift pressure and uplift pull test standards to ensure that “Mechanically attached assemblies tested . . . shall resist a minimum uplift pressure of 60 psf (2.9 KPa) when tested by the FM Approvals Uplift Pressure Test procedures . . . without release from the deck, and shall be maintained in place.” The current, relevant UL and FM Global Approval Standard uplift test standards are incorporated herein by reference. Other industry standards also provide for testing roofing installations against conditions corresponding to hail, standing water, foot traffic, fire, and corrosion.
The FM Global Approval Standard #4470 defines “wind uplift” as:
The force generated by wind on a roof system or components in a roof system resulting from wind-induced pressures. Wind that is deflected around and across the surfaces of a building causes a drop in air pressure immediately above the roof surface (negative pressure); the air in the building will flow beneath the roof deck (positive pressure), and the combined uplift pressures tend to lift the roof upward. Wind uplift may also be caused by the introduction of wind underneath the roof edges where it can cause the roof assembly to pull away from the substrate. Roof loss by wind can be avoided, or prevented, by proper installation and adequate adhesion, attachment, or ballasting.
New roofing constructions and methods are sought to provide cost-effective installation and satisfactory uplift load resistance. Similarly, new constructions and methods are sought to retain other exterior construction materials, such as shingles and siding, to buildings or other structures.